(1) Technical Field
The subject invention relates to a method of making a cam shaft for use in internal combustion engines in which cam lobes, bearing journals, and the like, are fixedly attached to a hollow tubular shaft resulting in a lightweight, strong, low cost cam shaft.
(2) Description of the Prior Art
Early in the history of the internal combustion engine, cam shafts were cast from iron in molds and then underwent numerous finishing processes until the cam lobes and the shafts were in precise orientation with respect to each other which facilitated precision valve control on the engines. Many improvements in the field have been realized since then and have resulted in the present state of the art.
Methods of making cam shafts for internal combustion engines which employ means for attaching lobes, bearing journals, and the like, to hollow tubular shafts are not unknown in the prior art. For example, U.S. Pat. No. 4,293,995 granted Oct. 15, 1981 to Jordan discloses a method of making a cam shaft for reciprocal piston engines whereby cams having irregularly shaped apertures are arranged on a hollow shaft and secured in a die. The hollow shaft is then widened by means of a rubber rod which substantially corresponds to the inner diameter of the hollow shaft. The rubber rod is compressed from both ends to cause the body of the rod to expand. The hollow tubular shaft is widened to such an extent that the outside wall of the shaft surrounded by the cam reaches into the irregular inner form of the cam producing a tight, secure, fit. In addition, the patent also discloses use of hydraulic or electrohydraulic expansion of the shaft.
The expired U.S. Pat. No. 2,892,254 granted on June 30, 1959 to Garvin discloses a method of making a cam shaft wherein the cam lobes are formed from the tubular shaft by the application of internal pressure to the tubular shaft while the shaft is contained in a die having cavities conforming to the shape of the lobes. The cam lobes are formed one at a time in sequence in the die by the application of hydraulic pressure within the tubular shaft such that the shaft expands into the cavities of the die thereby forming the cam lobes.
Inherent with methods of making cam shafts for internal combustion engines from tubular shafts are the associated problems with expensive and elaborate piston cylinder arrangements utilized to create sufficient hydraulic pressure within the tubular shaft to expand the shaft outwardly. Employing high internal pressures also requires the use of expensive dies and, in addition, sealing problems often arise.
Another method has been to drive a ball or mandrel of larger diameter than the interior diameter of the tubular shaft to expand the same into engagement with the interior apertures in the lobes. This method requires close tolerances in the lobes, tube thickness and mandrel or ball.
The present invention overcomes all the aforementioned problems while facilitating the production of a relatively low cost, high quality cam shaft which is also very strong and durable. Significantly, the lobes of the cam shaft may be made of different materials from each other and from the shaft itself.